Batteries

[BrizzleBoy]

Tried to post this in technical section but wouldnt let me.

Before I start I profess to know next to nothing about rechargable batteries. I will now go on to prove it...

As I am hoping to be able to buy my ebike through salary sacrifice ( no income tax, no vat, no money back , no guarantee ) if the rules allow it I am thinking of buying an additional battery at the same time to take advantage of the savings.

Now to the technical bit - will I have problems if I leave this battery ( uncharged as it arrives I guess ) until my original battery gives up the ghost. Or is it a silly idea?

Thanks

 

[flecc]

Definitely don't buy a second lithium battery of any type, as they age at a constant rate whether used or not. So that means Li-ion, Li-poly, Li-manganese etc.

It's also best not to buy a second NiMh battery if it's not necessary, since they lose capacity at about 1 to 1.5% a day and must be recharged every two months at least to keep them in working condition, thus gradually wearing them out.

So unless you intend to use both for longer range, best not to buy two.
.

 

[BrizzleBoy]

Thanks Flecc, advice taken no second battery will be bought.

Have just been reading another thread where you were suggesting Nimh batteries were far more reliable than Lithium Polymer. Just when I thought I had made a decision .....

 

[flecc]

Depends on territory and bike power though. In a fairly flat area, and/or with a low powered bike, there's a lot to be said for lithium batteries, good performance and range with easy charging rules, just charge at every opportunity.

But if there's long tough climbs to be done, especially with a powerful bike, and especially if the rider isn't a strong cyclist, lithium can spell trouble and short life, and that's where NiMh come in. They can work anywhere in any circumstance, albeit with a slightly lower performance and capacity, and they do have some special rules relating to charging.
.

 

[BrizzleBoy]

Thats really useful information - thanks again flecc.
Looks like Li-Poly will be right up my street.

 

[Lesley]

Hi Flecc, first time poster! I have learnt so much from reading your various advices on here. Can you please say in more detail what the "special rules" are that relate to NiMh battery charging compared to Li-ion ones, thank you

 

[flecc]

Certainly Lesley.

NiMh battery cells still have a residue of the "memory effect" that was a problem with the preceding NiCad types. What this meant on NiCads was that if they were charged when only half discharged, they could chemically "remember" the point at which that charge commenced and sometimes refuse to issue current below that point. Obviously that could greatly reduce the capacity of a battery, and therefore the range that a bike had.

There's only a very slight tendency for that to happen on NiMh batteries, and it's easily prevented. All they need is from time to time have their content fully used up before the next charge. The way in which this is organised isn't critical, but around once a month or once every ten charges or so is ok.

Of course it's extremely inconvenient to ride an e-bike until the battery runs out and then have to pedal it home without power, so that's generally avoided in various ways. Some have a spare battery with them when they do the "emptying" trip. Others get used to their bike's range and run it very close to the empty point, also using the bike's battery meter to judge the remaining charge, and that's also good enough, taking it to cut-out not being vital. Some e-bike manufacturers thoughtfully supply chargers which have a discharge function, sometimes called "refresh", and with that a battery already fairly low can be discharged with the recharge automatically commencing afterwards, and that's best of all of course.

However, NiMh batteries should never be independently discharged with resistors or a lamp until empty, since being truly empty can destroy them and prevent acceptance of charge. The bike's controller and chargers with a discharge function just discharge down to about 1.1 volts per cell, a safe level from which they can recharge.

So in summary, all that's necessary is to run the battery to cutout or near to that on the bike or suitable charger, once in a while.

P.S. Thanks for this question Lesley. I've posted the content of the above in the Battery FAQ section for other's future reference.
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[gkilner]

Sealed Lead Acid Battery

Hi Flecc, whilst on the subject of batteries, do you have any advise regarding good practice with charging the old Lead Acid batteries? - as used on my Powabyke.

I currently do a daily commute to work, totaling approx 13miles, charging the battery each evening after work. I've never let the battery run any lower than midway on the power guage, would it benefit from being discharged further?

Thank you,

Gavin.

 

[flecc]

Not really Gavin. Lead acid is the oldest technology of all of course, and it's also the most forgiving of what we do with it. The only thing to avoid is leaving them without charging for three months or more, which causes permanent sulphating of the plates, lowering the capacity.

Keeping yours up to charge all the time is fine, and it's what happens in our cars, where batteries last up to five years these days.. Sadly they don't last that long on our bikes though, the controllers being a bit too rough with them for that.
.

 

[ltn_wx]

Hello Flecc, another first time poster!

May I ask what the difference is between Lithiom Ion and Lithium Polymer?

Many thanks.

P.S. Forgot to mention Lithium Manganese.

 

[flecc]

They are all lithium-ion, Li-ion for short, ltn_wx.

The references to cobalt or manganese concern the materials used in the all important cell cathode, manganese being the safer.

Polymer, poly for short, refers to a different way in which the electrolyte is constructed. This was originally meant to give fast charging, but has been changed to give a bit more capacity instead. Li-poly are more suited to low power motors.

We will shortly be seeing yet another Li-ion type, LiFePO4, with the confusing name Lithium Iron. These will use iron as the basis of the cathode construction as it's theoretically the best material for that, better than any other element. As ever, design life is never easy, so there have been problems to overcome in achieving those, but the first low powered one is on the market so we are making progress.
.

 

[ltn_wx]

That's great - and many thanks for such a speedy reply.

 

[Lesley]

Many thanks for your reply Flecc, sorry for late response, wasn't able to log-in yesterday! I have a discharge switch function on the battery charger so will use that. It's down to mid range at the moment - hadn't used the bike for a little while and it was still on full charge when I took it out so was impressed with that!