Bosch Dual Battery questions

Electrically assisted bikes, trikes, etc.
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Bosch Dual Battery questions

Postby pcoghill » 23 Jul 2020, 1:14pm

I'm new to eBikes and have a couple of questions about managing the battery. I have a Bosch Dual Battery system with two 500 Wh PowerTube batteries and a Kiox display. They seem perfect for my requirements but...

  1. What happens if I completely discharge both batteries on a ride? Will I ruin the batteries? I have got down to 6% remaining when I got back home and I didn't want to try an experiment without finding out if the BMS could cope.
  2. Does the available energy drop off suddenly when the batteries get close to full discharge like in NiCads?
  3. Will it damage the batteries if I charge just one of them from, say, 20% up to, say, 80% when I'm at a cafe. Can the system cope with one battery at 20% state of charge and one at 80% or do I have to remember to try to balance the time each battery is receiving it's top-up charge?

Any advice will be greatly appreciated because otherwise I'll just risk it.
Last edited by Graham on 23 Jul 2020, 2:19pm, edited 1 time in total.
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Re: Bosch Dual Battery questions

Postby Jdsk » 23 Jul 2020, 2:22pm

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Re: Bosch Dual Battery questions

Postby stodd » 23 Jul 2020, 2:28pm

The BMS should prevent damage from complete discharge; it should cut out before the battery gets to danger level. Still, probably best not to get too low too often.

The energy does drop of pretty quickly near the low levels. See for example ... %20UK.html
(graphs for many different cells available, not sure that those batteries use but the overall graph shape is pretty similar).

I think (but not sure here) the system swaps between the batteries rather than using both at once; so in that case it would just use the charged one till it got below the other.

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Re: Bosch Dual Battery questions

Postby Lodge » 25 Jul 2020, 6:15pm

If the PowerTube battery system is the same as for the older style 500 Wh frame batteries then yes, the Bosch electronics use each battery in turn. On my R&M Delite you can see that it uses 20% from one before swapping to the other, then back again when the second has used up 20%. And so on. Therefore charging just one battery over lunch should not be a problem.

You must be going some to use up nearly 1 kWh. Enjoying turbo mode no doubt (I full agree it's great fun). I've not yet managed to get my Delite to use up both batteries even with a 60+ mile ride with a couple of thousand feet of climbing.

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Re: Bosch Dual Battery questions

Postby pcoghill » 25 Jul 2020, 6:58pm

You're correct I spend an embarrassing amount of time on "Turbo". My excuse is that I'm down to 47% (ish) lung capacity - not due to the coronovirus I might add - and an ebike is the only way I can keep up with my old cycling buddies. I have to say I love the bike, although I still feel a niggling sense of cheating when I click onto Turbo - I'll grow out of it I'm sure.

I'm being really careful while the SARS-CoV-2 virus is around and not riding with anybody apart from my partner (also on and R&M dual battery ebike). The best I've managed so far is 95 km and 1900 m ascent, but like I say I use Turbo a lot.