Q about adding second battery to eBike. (Not sure which best forum).

WIAWSNB

Hi.

Giving thoughts to getting a G-Tech City ebike*. Yes, I know it's discontinued, and I know that parts will become scarce, and that's one of the reasons for this Q.

Apart from the rubber/carbon drive belt, the other unique part is, of course, the battery. The battery isn't really a problem as such, as to have an eBike battery reconditioned seems to cost less than a new one anyway (£300 new?! lawdie!)

But, the main issue at the mo' is to extend capacity = range. So, my thoughts were to add a DC socket to the battery case, wired directly across the 36V outlet pins. Then a second 36V battery can be mounted on a carrier, and plugged in to 'double' the range.

Yes? No? Ta 😶

*Why this model? There happens to be one in VGC available locally, but it's mainly because of its design, being almost a normal bike and 'only' 16kg. Against this is its single-speed, which I why I'd need to ensure range is more than adequate; if it were to conk out, wife would conk me out too.

JSmithy45AD

They apparently use their own propriety communication pins, the best and easiest option is to just carry a 2nd battery and swap them out as necessary.

WIAWSNB

https://forums.moneysavingexpert.com/discussion/comment/81994047#Comment_81994047

Thanks.

New batteries are unavailable, and cost £300 when they were.

Yes, they have their own pin design, with the outer two (of four) carrying the power. So it would be an easy task to wire.

All I'm asking is if there is anything amiss in my plan. Ta.

forgotmyname

What battery management do they have?

How are you going to prevent a voltage discrepancy between the two packs? The two packs are unlikely to
to be identical, that can cause one pack to drop faster than the other and then you have the 2nd pack
fast charging the first pack with no limitation in the amount of current except the cable wiring.

Yorkie1

There are not infrequent reports of fires caused by battery / ebike / escooter issues. Are you sure it will be fire-safe?

WIAWSNB

https://forums.moneysavingexpert.com/discussion/comment/81994985#Comment_81994985

By having it permanently connected whilst in use - the voltage drop should be even.

WIAWSNB

https://forums.moneysavingexpert.com/discussion/comment/81995036#Comment_81995036

Not any more likely to burst into flames than if using only one battery - it'll be unplugged when off and stored.

And if it bursts into flames whilst riding, well, that will be exciting - great balls of fire 🔥

forgotmyname

https://forums.moneysavingexpert.com/discussion/comment/81995185#Comment_81995185

No they don't work like that, one pack or even one cell in a pack may produce less power than others in the pack.

Think of it as 100 people all digging a hole, some work faster than others some can carry more than others and some get tired faster
than others.

That's the batteries in a pack, good brands do match them but it's common for a single cell in a pack to fail whilst the rest are
fairly healthy. That one weak cell causes issues for the whole pack. It gets hotter than the rest and drains faster than the rest
which is why you need good battery management.

WIAWSNB

Both batteries would have their own individual management.

The two 'managed' outputs would then be joined in parallel.

JSmithy45AD

https://forums.moneysavingexpert.com/discussion/comment/81994389#Comment_81994389

So you already have 2 correct batteries? Your best bet is still just to swap them.

WIAWSNB

https://forums.moneysavingexpert.com/discussion/comment/81995578#Comment_81995578

No, only one correct battery - and they are no longer available. But would like just to add a second generic 36V Li-ion battery to boost range.

The 'real' battery costs £300, not that I can get one. A similar capacity battery should be gottable for a third that.