CTEK CS Free review | Portable battery charger and booster

Date reviewed: July 2022 | Tested by: John Milbank | RRP: £280 | www.ctek.com/uk

The CTEK CS Free on review here is a car and motorcycle battery charger and a booster, with its own built-in battery that can have it pump enough power into a flat battery in just 15 minutes to have you on your way. It’ll work with 12V lead acid and lithium batteries, and there’s even a solar panel available that will juice it up in in about half a day.

I’ll admit I was sceptical, but the CTEK CS Free really does work very well indeed. There is one issue with motorcycles that potential buyers need to be aware of though. I’ve been using it for two months, testing it thoroughly on a 12Ah motorcycle battery to see whether it’s worth the money…

CTEK CS Free features

The CTEK CS Free is a genuinely versatile device, with several useful features:

• It’s a boost charger, which can use its internal 11.1V, 6,000mAh lithium-ion battery to rescue a flat bike or car battery in just 15 minutes, giving it enough power to start a healthy engine.

• It’s a maintenance charger that can keep a battery in peak condition when not in use.

• It works with 12V lead-acid or lithium batteries from 10Ah to 130Ah.

• It can be charged via an optional solar panel, or from another 12V battery using an optional cable to connect to the terminals, or via a cigarette lighter socket with another cable.

• It’s got a USB-C outlet that’s powerful enough to charge a laptop, being capable of outputting 5V to 20V at 3A

• It’s got a USB-A outlet that’ll supply 5V at 2.4A.

The CS Free comes with a USB-C PD (Power Delivery) wall supply (and a choice of worldwide plugs), which automatically outputs 5V, 9V, 12V, 15V or 20V, each at 3A. This charges the unit’s built-in battery, and acts as the power supply when the CS Free is used for maintenance charging.

Alternatively, you can use the optional 60W solar panel to power the charger when it’s in maintenance mode, or to recharge the internal battery. Be aware though that this measures 422mm x 537mm when folded up (it’s 20mm thick), so it’s not practical at all to carry on a motorcycle, and it’s not cheap at £320.

The charger itself is IP54 rated, meaning it’s protected against dust ingress for 2 to 8 hours, and water splashes from any direction, so if you leave it outside for solar charging, it should be safe tucked under the tent that the panel and its carry case forms.

The USB-A socket can deliver 2.4A, while the USB-C is a PD outlet

The main feature of the CTEK CS Free is its boost mode, which analyses the state of a flat car or bike battery, checks whether it’s lead-acid or lithium, then spends 15 minutes pumping the energy from the built-in battery pack through a set of well-made crocodile clips, leaving the motorcycle, car, quad, jet ski or whatever, ready to start.

Keep in mind though that the CS Free is designed to work with batteries from 10Ah capacity, so isn’t suitable for the 8.4Ah pack found in the Honda MSX 125, for instance, or the 6.3Ah one in the Yamaha SR125. Of course, it could be argued that these should be fairly easy to bump start if the battery’s flat.

Having the ability to power laptops and charge other devices is a fantastic addition, and could be a major selling point for many buyers, though devices like the outstanding Omnicharge 20+ are in many ways superior for this sole purpose, and that has a slightly larger power capacity of 71Wh, compared to the CS Free’s still impressive 66Wh.

Inside the CS Free is this 6,000mAh battery. The fact I could get it out (though it’s not designed to be disassembled) indicates it could be replaced down the line, but the serial numbers on the pack didn’t lead me to any replacement parts. It’s also unlikely it would be financially viable for CTEK to replace depleted batteries.

The CS Free’s internal battery should hold a full charge for up to 12 months, will charge in an hour using the included power outlet, and has a life span of 300 cycles before it’s at 80%. This is worth noting if you’re intending to use it a lot for powering a laptop and charging accessories, as while these are fully depleted cycles that won’t be affected if the charger is connected to the mains and used for maintenance charging, once the battery is heavily worn it’ll struggle to act as a booster.

Most motorcyclists buying a charger will be using the maintenance mode almost daily, and the CS Free has an LED display showing an estimate of how many hours it will take for a relatively healthy battery to be completely charged, then runs through a standard cycle to bring the battery to its peak, and to keep it there. The ability to do this from the optional solar panel is particularly tempting, though of course it’s not going to pay for itself for many years when compared to the cost of buying and using a simple maintenance charger like the £42.99 Optimate 1+ Duo, which has added lithium charging capability to its features since our review.

The CTEK CS Free is extremely versatile, and very well made, but the maintenance mode is let down by one key point for riders…

CTEK CS Free connections/h2>

There is no fly-lead available as an accessory for the CTEK CS Free, which means the only way to charge a motorcycle battery is to take the seat or battery cover off, and connect the crocodile clips.

CTEK told me that the high current output of the CS Free in boost mode (up to 20A) means a fly lead that’s rated up to 10A isn’t beefy enough. This could mean that as a maintenance charger it’s unusable for some riders, and inconvenient for most.

You might consider making up your own fly-lead, and as the CS Free’s output socket is a standard XT60 male connector, this wouldn’t be difficult with a female connector and some basic soldering skills. Using an inline 5A fuse should give the protection needed in case the CS Free were to be inadvertently put into boost mode, but it would of course be entirely at your own risk.

Some bikes, like the BMW R1250GS for instance, have a remote live connection to the bike’s battery, only the negative being accessible. This should likely be capable of carrying the current in boost mode, but you need to check your own wiring first.

The solar panel is extremely well made, but you’ll struggle to carry it on a bike

CTEK CS Free solar panel performance

When plugged into the mains, maintenance mode performs as expected, with simple progression of the ring of LEDs, so it really is a shame that there’s no option of a fly-lead from CTEK.

The 60W solar panel can be very effective, even in Britain. I placed it in the garden pointing south at 08:30 when it was clear and sunny, but it soon clouded over; the day was patchy, but still, when I checked six hours later, the CTEK CS Free was already fully charged after being completely depleted. Impressive.

The solar panel’s bag forms a shelter that provides adequate protection for the charger and battery when outside

Rated at 60W, the panel outputs about 20V at up to 3.5A. Using an inductive current meter, I measured around 0.5A in cloud (10W) and 1.9A in direct sunlight (38W), though of course this will vary depending on where you are and the weather conditions.

I also tried charging the bike battery when it was at 11.4V (so low, if not flat) from the CS Free while it’s internal battery was full and it was connected to the solar panel. At 16:30 on a cloudy July day I set it all up; boost mode wasn’t activated, but the internal battery was clearly used to add charge to the bike pack, as at 6pm the CS Free was flashing its empty light, and the bike battery was at 12.8V. At this point there seemed to be no charge going into the CS Free, so I left everything under the solar tent to see what happened…

The design of the panel’s carry bag means it creates a shelter for the charger and the battery when erected, so I wasn’t worried leaving it out when it got stormy that night.

The next day started cloudy, but at midday the first segment of the CS Free’s internal battery status was flashing, showing that the CTEK was taking a charge for its own pack while charging the bike battery, which had reached 13.3V (it showed 14.3V being pumped in at 0.9A with the crocodile clips connected).

The solar panel can charge the CTEK CS Free quickly, as long as nothing blocks it

An hour later the sun was out and the CTEK’s own battery was approaching half full, while the bike battery status still displayed >8 hours. But by 15:00 the bike battery was fully charged, and the CS Free was flashing the final quarter LED for its internal pack. By 16:00 it was all done.

Leaving it connected, by the next morning the CTEK’s internal battery had dropped to about half charge through maintaining the bike battery and keeping all its own LEDs illuminated. The solar panel brought this back up, but I’m not sure that using solar energy to keep a bike constantly on maintenance charge is the best bet as it’ll be cycling the CS Free’s internal pack daily – in two years, the lithium-ion cells inside could be well past their best. I’d not be too worried about it keeping a healthy pack in tip-top condition in the poor light of winter, as even if it does struggle for a day or so, it should recover well before the bike’s battery depletes too far.

Realistically though, the solar panel is not intended for permanent use, so it’s far more suited to travellers heading to remote areas, which rules bikes out as it’s too big to carry.

CTEK CS Free boosting performance

The CTEK CS Free is NOT a jump starter – it cannot be used to fire up a dead vehicle, despite its large capacity internal battery. Instead, it uses an ‘adaptive boost’ function, which gets all that energy into a flat battery in just 15 minutes.

To test it, with a full internal battery on the CS Free, I took a new 12Ah PTX12-BS Powerline battery (the same as fitted to my 2001 Honda VFR800), and flattened it using a halogen H4 bulb that drew 4.8A. With the bulb connected but no longer lit after a few hours, the bike battery showed just 0.18V, while with the bulb removed it settled to 5.8V with no load. It was flat.

I then connected the CTEK CS Free to the dead battery and it immediately started putting out 14.2V, peaking at a current of 17.82A. 15 minutes later, the battery was warm, the charge level LED ring on the CS Free was flashing just one segment to say it was flat, and the main charging time ring displayed ‘start’.

And start the bike it did – I connected this battery and the VFR fired up no bother at all. In fact, I stopped the bike and restarted it several times with no problems; this certainly had pushed enough power in to get me on my way.

I also flattened the battery again, then charged a GoPro using the CTEK to use some of the internal battery’s power. Despite this, boost mode still fired up fine. I disconnected the charger after a few minutes and left it, knowing that the internal pack was now well below full, but when I reconnected it, it still went straight into boost mode until it was empty, leaving the bike battery ready to work.

Why not just use a jumper pack?

With jump starter packs like the Noco GB40 costing about £100, the CTEK CS Free might seem expensive, though it’s worth noting that the GB40 has a much smaller 11.1V, 2,150mAh (24Wh) lithium-ion battery inside it, and it can’t act as a maintenance charger; it’s purely a booster pack.

Of course, the GB40 and a decent maintenance charger can be had for a total of about £200 pretty easily, but I’ve never tried a Noco booster pack so can’t comment on its effectiveness. It does claim to deliver 1,000A, but it’s the Cold Cranking Amps (CCA) that really matter, and this isn’t listed. Apparently, it’ll boost a petrol engine up to 6.0 litres, so it shouldn’t have any problems with a motorcycle.

I asked Tony Zeal, training manager at CTEK in Sweden why the company believes the CS Free’s method of rapidly charging the existing battery is better; “The CS Free first tests the battery to establish its size and amount of discharge,” he told me. “It will calculate how much current is required to charge the battery within 15mins, then as it initiates ‘adaptive boost’ it can use up to 20A, trying to get the battery to a point at which it should (by the charger’s own calculations) be able to start the vehicle.

“It may seem a large amount of current, but over a short period of time it is safe, especially when compared to a jumpstart pack, which acts as a replacement for the battery, not trying to charge the battery as the CS Free does. When you disconnect the jump start pack the alternator will ‘see’ the massive black hole that is the flat battery, and tries to meet the demand, which leads to a spike in both voltage and amperage, potentially causing electrical system damage.”

Of course, this could be the same situation you’d find when jump-starting a motorcycle or car using jump-leads. Personally, I’ve always left the leads connected for a good few minutes after jumping, and have had no issues, but I also haven’t had to do it on any bikes with the latest CANbus looms and multiple ECUs.

According to the National Roads and Motorists Association in Australia (NRMA), incorrectly jump-starting a car can “zap” the electronic control units in cars if not done correctly, though the RAC says that “it should be safe to jump-start your car with either another vehicle’s battery or a portable battery pack”. The AA states that removing the jump leads while the car engines are running can “cause serious damage to the cars’ electronics”.

Ultimately, CTEK’s solution is designed to get a bike or car running again with the minimum of fuss and risk. The CTEK CS One we reviewed recently had a similar design focus, being intended to make charging as simple as possible.

I’m not in a position to say that one method of starting a dead bike or car battery is safer or better than another, and it’s true that a dedicated jump-start pack is typically a lot smaller and more portable than the CS Free, so I can only report on my findings during testing.

CTEK CS Free control

There’s little to worry about on the CTEK CS Free – it’ll start charging as normal when connected to the mains, another car battery or the solar panel, with the six-segment LEDs showing roughly how long it’ll take until the battery is in peak condition. It’ll then maintain that battery until you need to use it.

The small button turns on the power bank, and shows how much juice there is in its own battery via four LEDs.

Having used the CTEK CS One, which has Bluetooth connectivity, I was surprised that this model didn’t also work with the dedicated app to allow you to see more detail of the process.

I was also disappointed with the instructions, which use pictures rather than words, and can take a bit of fathoming. Given that the spec and warranty info is written in English, I’d have liked to have seen some clearer explanations of what everything means.

The CTEK’s well put together, with the lithium battery protected at the base of the unit

CTEK CS Free review: Verdict

TLDR? There was a lot of testing and tech-speak in this review, so if you’ve skipped to the end I’m offended, but can tell you that the CTEK CS Free does work very effectively, delivering on all its marketing promises.

The lack of fly-leads is a real shame for motorcyclists, who’d no doubt want to use the maintenance charging features of this device in order to keep the battery at its best when the bike’s left unused for a while. Of course, some might consider making their own lead, and with a 5A or perhaps 10A fuse fitted, there should be little issue with this.

I was shocked at just how effective the solar panel is, but needless to say you’d seriously struggle to carry it on a motorcycle, so it’s not really going to help when away on tour. The bottom line is that the CTEK CS Free is a very impressive performer, but you do need to consider how and where you’ll use its features. There’s no doubt thought that it could get you out of trouble in an emergency, that it’s handy for keeping other devices charged, and that it can be kept powered up effectively for free if you invest in the solar panel.

The CTEK CS Free is brilliant for those travelling by car, minivan, camper van or RV, and if you’re a motorcycle rider that wants something to use across other forms of transport it’s worth considering; it’s just lacking as a bike maintenance charger, the bread-and-butter for most riders.

There are more useful motorcycle maintenance chargers, and better value and performing portable power banks, but it’s fair to say that I’ve never come across something that combines them both, and that can get a flat battery up and running again so quickly. You never know when that boost function could be essential...

Be sure to regularly check for discounts available through BikeSocial membership – members save 10% at Halfords, which is one of the retailers for this charger.