Hi, I'd like to increase the battery capacity of a project, but the space inside of the underwater housing is limited, so the form factor of batteries is important. At the moment I've got the space for 2 thin batteries, but not one battery that's twice as thick.
I'd initially planned on wiring a couple of 3.7V batteries in parallel, but have read that for lithium batteries that this is a really bad idea. I've tried to find information on wiring them in series, but the results all seem to be suggesting that either 1)it's fine, and 2)don't try to charge them in series. Considering that there's a lot of webpages that suggest wiring them in parallel is also fine, I was hoping someone who knows can advise. I'll also be using a powerboost to increase the voltage to 12V anyway, so it doesn't make a difference on that side.
Yes, it should be fine to connect them in series. As mentioned, you cannot charge them likes this, you will have to remove the batteries for recharging.
I think you mean a voltage boost. These modules cannot boost the power, that would break the laws of physics! If anything, they reduce the power a little because they are not 100% efficient.
Li batteries can be placed in series and parallel and series parallel.
If 2 Li batteries are wired in series that is known as 2S.
If 2 Li batteries are wired in parallel that is known as 2P.
If 2 sets of Li batteries are wired in series then those 2 sets wired in parallel that is known as 2S2P.
Li batteries wired in parallel can be charged together, li batteries wired in series can be charged together, li batteries wired is series parallel can be charged together with the proper BMS.
Li batteries wired in parallel should be brought to the same chemistry. Charge each Li battery to be placed in parallel individually. Once the individual batteries are charged, connect them together in parallel, not connected to any load and let them sit there for 24 to 48 hours while the batteries chemistry comes into equilibrium.
Make sure the batteries are all bought at the same time.
A 2S grouping would use a 2S BMS. A 2S3P, 2S4P, 2S5P and so forth grouping would use the same BMS as a 2S grouping. Charge times increase for each parallel branch added.
Almost forgot once the parallel batteries chemistry is equalized then treat those batteries as one single battery for charging purposes. Meaning no need to take them out and charge them individually again.
When the manufacture makes a batch of batteries they use a large mix of battery sauce containing lithium. The lithium used to make a large batch of batteries has the same chemistry throughout the batch. Typically when buying 10 lithium batteries at the same time those 10 batteries were made using the same batch of lithium mix. Those batteries are prime for chemestry matching.
Where as if I bought one LiPo today and in 6 months bought another LiPo then there is a high chance that the Li mix is not exactly the same. Those batteries are not prime for chemestry matching.
Not saying that you cannot connect those 2 batteries together in parallel.
If both batteries are sitting on a shelf and I buy one on Monday and one on Tuesday, I'd use them in parallel. If I bought one on Monday and bought another one 2 months later after a stock rotation, I'd not connect them in parallel.
I put Li batteries in parallel all the time. In fact I am working on a 1000W solar battery charger right now and am using 4 20Ah LiPoFe4's in parallel.
