I've seen the R&M Delight ebike with dual batteries connected such that they are both being used simultaneously (i.e. no A-to-B switch) but I am not aware if they have to be the same capacity (i.e. both 400wh or 500wh). Does anyone know if two battery packs of the same voltage but different capacities can be connected in parallel on these or other ebikes? I would assume they would draw down / remain balanced even if not the same capacity).
Dual Batteries on an eBike ... ????
- Thread starter Ken M
- Start date
6zfshdb
Well-Known Member
- Region
- USA
- City
- Northeast Pennsylvania
As long as the two battery packs contain the same type cells with the same internal resistance, they should draw down evenly despite having different capacities. To me, having an A/B switch makes more sense though. Without a switch, taking a short ride means you have to charge two partially discharged batteries instead of just one. This means having two chargers or charging the batteries in succession which takes twice as much time.
Bruce Arnold
Well-Known Member
Capacity makes no difference in this application. Basically you've put two batteries of the same voltage in parallel. The system thinks it's one large battery.
michal
Member
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- USA
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- Brooklyn, NY
R&M's dual batteries are actually charged simultaneously when you charge them on the bike. Also, wouldn't using the batteries simultaneously prolong their lifespan?
https://www.r-m.de/en-us/technology/dualbattery/
This is an important aspect I wasn't really considering. I'm assuming you are correct that the packs MUST have the same cells with the same resistance or there could be some impact on pack performance and/or life given that they will not draw down evenly. I was kind of assuming that if I added an extra pack it would have identical cells even if a different capacity but I could envision that it would be nice to say add a same voltage pack on rack that has 21700 cells while the frame battery pack had 18650 cells.
It sounds like this would be a bad technical combination unless I went with an A/B switch. Thanks for any additional feedback.
Feliz
Well-Known Member
Correct
Alaskan
Well-Known Member
It is my understanding that a Bosch powered bike with a two battery set-up is programmed to draw 5% from one battery and then 5% from the other, back and forth till they are drawn down. Although they may charge simultaneously ( I seem to recall that they actually charge in sequence, first one to full charge and then the other), they discharge in back& forth sequence. Perhaps @Court or an expert Bosch bike dealer like @Chris Nolte can set the record straight on this.
Hi Alaskan, this is a bit more interesting than I expected. I thought two battery packs of the same voltage could potentially be connected in parallel and utilized and charged as connected without an A/B switch but seems it's not exactly common knowledge if this is OK or not. I certainly don't want to damage two expensive packs but i like the idea of expanding my range occasionally by having two packs.
My assumption was that the BMS in both packs would protect the packs by ensuring each achieve balance when charged fully and dynamically protect them when being drawn down. Maybe Bosch has a more advanced BMS that R&M is taking advantage of on some of their dual pack ebikes.
This is ideally what I was hoping was true....thanks. Will be interesting to see if others have specific technical concerns...
Alaskan
Well-Known Member
A word of caution: Bosch ebikes are similar to Apple computers. They work, with very long, mean time between failures. This is as much from software/firmware as from engineering. As such, I, a dedicated do my own maintenance guy, would avoid making any wiring changes or installation without Bosch approved wiring harnesses and equipment compatibility checks a well as firmware module loading. Just like Apple, they discourage do it yourselfing on their gear and void warranties for any unapproved tinkering. They have great parts distribution and technical support resources but are rigorous about what can and can't be done and the how of it as well.
JRA
Well-Known Member
The Grin CA3 display has an A/B battery selection feature. It even allows one to use batteries of different voltages and chemistry and tracks wh’s used overall and charge cycles for each.
For this ride I used a 10ah 48v LiFePo4 Whale pack and a 17ah 52v LiMn brick pack in the frame bag.
For this ride I used a 10ah 48v LiFePo4 Whale pack and a 17ah 52v LiMn brick pack in the frame bag.
Over50
Well-Known Member
This is probably answered and redundant but: I dont think they use or charge simultaneously but rather switch between in increments . Very good software... I have 4 Bosch bikes and 2 are dual battery. I can ride w any combination of 1 battery, 2 batteries of 400 or 500 wh. I have 2 packs of 400 and 2 of 500. I often use 2 400s or 1 500 and 1 400. Just depends on what I have charged up when I go out. For cold weather commute I just take 1 fully charged 500 such that I can take it inside and charge at my desk. Then I avoid carrying 2 batteries or leaving 1 on the bike all day in the cold. For fair weather commuting I use 2 batteries and leave them on the bike. Often I only charge them to about 80% as I dont need all the range of 2 batteries fully charged.
6zfshdb
Well-Known Member
- Region
- USA
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- Northeast Pennsylvania
The R&M system may prolong battery life but it still takes twice as long to charge, even on the bike. 4.5 hrs for one, 9 hrs for two.
Alaskan
Well-Known Member
If you think about it the answer is quite obvious.
500 watts is sufficient for most people's daily ride. I use 2-500 watt battery packs when going on a long ride, when the ride has a lot of elevation gain, etc. The smaller battery pack fits nicely into my trunk bag. Mostly I ride with just the one 500 watt battery.
I would rather not have to carry around the extra 6 pounds of battery for every ride when I know I won't be needing the extra electrons. If the bike were offered with one 12 pound 1000 watt battery or two 6 pound 500 watt batteries, I would choose the two battery set-up.
Alaskan
Well-Known Member
If you anticipate having to recharge both batteries quicker than 9 hours, buy a second charger, remove one battery from the bike and charge them both simultaneously. Problem solved.
6zfshdb
Well-Known Member
- Region
- USA
- City
- Northeast Pennsylvania
I'm not knocking the R&M design. It's a well engineered yet expensive system. In my case, I would rather put the money in spare batteries and an extra charger. I use the one with a suitable capacity for the ride I plan. Like you, I would rather not carry the extra weight if it isn't needed. For longer rides, I throw a spare on the rear rack and swap when necessary.
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