Technological developments often arrive unexpectedly. No offence intended, but we were surprised to see Dahon taking (and still, to date, holding) the honours for lightest production folding bike, and we were equally surprised when a lithium-ion Powabyke Shopper turned up on our doorstep.

For those unfamiliar with such things, Powabyke build reliable, if rather lumbering electric bikes, and the 24-inch Shopper is probably the least exciting of the lot. Lithium- ion batteries were expected to revolutionise traction applications a few years ago, but they didn’t, largely because charging complications made the larger batteries liable to set afire, resulting in some high profile conflagrations. At least one manufacturing plant has burned down, and computers, cameras and electric bikes have exploded – notably the EV Global Mini E-Bike, 2,000 of which were recalled in America.

Without getting too technical, Li-ion batteries don’t like being over-charged, over- discharged or over-heated. Make a mistake (let’s face it, we all make mistakes) and the battery is liable to tip over the abyss into thermal meltdown – the sort of thing that used to happen to the engines on the Star Ship Enterprise. As lithium reacts violently with water, the only course of action at this stage is to run away as fast as possible.

…This is neither the most fashionable nor effective of bicycles…

Problems are rare with individual cells (in digital cameras, for example), but a 36 volt electric bike like the Powabyke needs ten large 3.7 volt lithium cells, and each one must be charged, discharged and monitored for temperature individually.This sort of thing needs a lot of control circuitry, but as usual the Chinese have driven down prices, which are now low enough for Powabyke to offer a Li-ion battery pack and charger as an upgrade option. If all goes well, it will soon be available on new bikes, and the intention is to offer a retrofittable upgrade on older models too.

So why bother? It’s all about energy density, or the amount of energy available in a battery of a given weight. Powabyke uses old-fashioned lead-acid batteries, which deliver around 30 watt/hours (Wh) per kilogram. In the 1990s, nickel-cadmium batteries became available, supplying 50 Wh/kg, and a few years later, nickel-metal hydride did better still, at 70 Wh/kg.Today, lithium- ion batteries with a capacity of 130 Wh/kg are coming on stream. Comparing like with like is a bit difficult, because different types of battery are tested in different ways, and casings, wires and electronics tend to level the playing field a bit, but weight-for-weight, lithium-ion should be at least two or three times as effective as lead-acid.The 36 volt lead-acid battery fitted to the Shopper weighs 14.1kg, and its Li- ion replacement, 6.4kg, despite being assembled into the same heavy casing. As we shall see, it goes further too.

Powabyke Shopper

First a quick look over the Shopper. This is neither the most fashionable, nor effective of bicycles, but it’s cheap (£539 single -speed, or £595 with a basic 6-speed derailleur), well equipped (battery lights, rear rack, front basket and mudguards), and it offers a low step-thru height of 37cm. In other words, it’s just the job for those who’re finding it difficult to get their leg over, but still want to ride to the Post Office and pick up a bit of shopping on the way home. If you can remember where you were when nice Mr Chamberlain met Herr Hitler, you will be in the target audience.

Complete with accessories, the 6-speed Shopper weighs some 25.9kg. Heave the 14.1kg lead/acid battery on board, and you’re looking at 40kg overall, which just happens to be the legal ceiling for electric bikes. Another gram and you’re nicked.

By comparison, the class-leading Lafree weighs from 22.2kg complete with delicately- crafted NiMH battery, and the chunkier Ezee Forza 25-29kg in NiMH form. Equipped with the new lithium-ion battery, the Powabyke still weighs over 32kg.

At 31″ to 62″, gearing is severely limited.That’s a reasonable bottom gear, but 62″ is only good for about 12mph at the top end, so your typical Powabyke Shopper will be passed by just about everything else on two wheels. Speed is not the object with this sort of machine, of course, but the lack of gearing makes it difficult to provide much human input when cruising along under power, because the motor runs up to about 14mph. That’s fine if you don’t want to pedal, but it will have a serious effect on range if you were hoping to. And sitting still in November means dicing with frost-bite, as we can testify.

Generally speaking, progress is noisy and slow. If you pedal with the motor turned off, it makes a loud tick-tick-tick noise like the cheapest sort of freewheel (presumably that’s exactly what it is) – turn the motor on and it whines loudly. Either way, progress is relatively laboured. But we don’t mean to be negative – the Shopper does what it does very well, and is currently Powabyke’s biggest seller.

Charging & Range

Powabyke claims the lithium battery will give a ‘non-pedalling’ range of 25 miles, and they’re dead right, because we managed 25.1 miles at 13mph, which is not half bad. Actually, it’s the furthest we’ve gone without pedalling by a fair margin. It’s a bit difficult to find the pedal-assisted range with a bike like this because long- distance rides are neither pleasant nor practical at 11mph. A reasonable guestimate for a more sensibly-geared bike would be 40 miles or even more.

Hill-climbing is a bit limited on the prototype, because Powabyke has restricted peak power to 250 watts, claiming that hill climbing is unaffected.Well, yes and no.We managed a 7% (1:14) gradient, but were disappointed to fail 10% without pedalling. Of course, the gears are so low that modest pedalling allows you to twiddle up 12% (1:8) or more without too much effort, provided you’re not in a hurry. Actually there’s plenty of grunt available – we’ve tested the lithium battery pack to 650 watts on another bike without meltdown, so it obviously works. And Powabyke promises that whatever output is chosen, hill-climbing will be the same as the conventional bike.

The charger is effectively ten little chargers in one, so it’s as big as a dinner plate, as noisy as a vacuum cleaner, and it weighs 2.6kg – definitely not a portable device. Charging is quite rapid – about 31/2 hours from empty to a full charge.Thereafter the power to the battery is cut off, but don’t leave the charger connected overnight, because the roaring noise doesn’t let up and it consumes an astonishing amount of power on standby. Look at it this way: charging the battery consumes a reasonably modest 600Wh, but leaving the charger plugged in for the rest of the night would add another 1,000Wh.

…at 26kg without a battery, the Shopper might be the wrong machine…

As the capacity of the battery is around 430Wh, charging is clearly a rather inefficient process, but we’ve seen worse, and the chargers are bound to improve.We should also point out that because of the way capacity is measured, those 430 Li-ion watts are much perkier than other types – think of it as a very big battery.

Conclusion

Powabyke expects to sell Lithium-ion versions of its everyday bikes for a premium of less than £150. If they can do this, the technology suddenly looks very attractive, because this battery will not only extend your range but give more charges. Lithium-ion batteries are claimed to recharge 1,000 times, against 300 or so for lead-acid. However, we think lithium-ion batteries only really make sense on a lightweight bike. At 26kg without a battery, the Powabyke Shopper might be the wrong machine to put it on.

The retro-fit battery and charger kit is expected to sell for £200, which makes sense if you want to upgrade a cherished Powabyke. But be warned, for technical reasons the control circuitry on an older bike may not allow the Li-ion battery to discharge fully, so you may not get the full benefit.

Now that the technology has been tamed, it seems inevitable that lithium-ion batteries will start to appear on lighter, smarter bikes (Powabyke clams to have a 25kg model in the pipeline). In theory, at least, this battery would give a really efficient electric bikes a cross-country range of 55 miles, with a recharge time of only 31/2 hours. In all fairness, the Powabyke Shopper is unlikely to be at the vanguard of the coming revolution, but it has broken new ground, nonetheless.

Specification

Powabyke Li-ion Shopper estimated cost £750 . Weight bicycle 25.9kg battery 14.1kg total 40kg Gear System Shimano 6-speed SIS . Gear Ratios 31″ – 62″ .Manufacturer Powabyke tel 01225 443737 mail sales@powabyke.com web www.powabyke.com