@couka So is it safe to put Li-ion batteries in parallel or not.
@Idahowalker final answer was good luck
If one pack goes soft then the rest are in jeopardy. Disagree?
In fact you should never separate them again.
Which raises the question of battery protection. If you use protected cells, then on a deep discharge they will trip the over-discharge protection at different points, which means when charging power is restored they will be at different voltages, which might not be a good thing. So that would argue for using unprotected cells and having a single protection circuit in the charger - like typical TP4056 modules. But then I'm not sure what happens if one cell fails in some way.
Most of my battery use is around solar. I use MPPT solar charge controllers that I program to shut off when the Vbatt gets to a voltage. I like the charge controllers to shut the load off at 11.0 volts which gives me enough time to notice that the Vbatt is low and the batt needs a manual charge. I found that shutting off the Vbatt at 10V's does not work so well. The charge controller will still draw V's from the batt when it has cut off the load. Most MPTT charge controllers have a LCD display and along with the other components will continue to drain a battery long after the load is shutoff.
I think you mean a voltage boost.
Yes, sorry, was looking into boosts for another project. I'm using a switching voltage converter for this.
You need to explain that statement
This aspect of the project is to use an arduino to control some lights in an underwater housing. The housing is a certain size/shape, wider than it is deep. The light elements need to go at the front of the housing. There is room at the back of the housing for something approx 8mm thick, so thin batteries, two next to each other (across the width of the housing). Unless I move a light element to the back, I can't fit a thicker battery. Moving the light element to the back will mean the light cannot get out of the housing.
You could also look at cutting down the consumption of your project - eg sleeping , using a different Arduino board , etc etc
The vast majority of the power consumption is the lights, and I need as much output as possible there.
Thanks for the replies everyone!
A single Lithium Ion battery can, and have caught fire, so on that basis just assume that no lithium battery is 'safe'.
The what?
I have dozens of Lipo batteries and routinely charge them in parallel. Nothing but Lipo cells in various S/P configurations as @Idahowalker Idaho walked us through above.
But you must be careful.
It's as safe as riding a bike in Paris. By which I mean the safety of using these amazing power sources is largely in the hands of the user.
Putting cells in parallel for use took some adjustment of my prejudices. Charging batteries in parallel was another sticky point for me. So I get the deep reluctance to do either. Some may not be able to get over it.
Users of Lipo cells are advised to know way more than everything there is to about the chemistry. A good place to start is
a7
The prismatic type of battery (flat pouch type) will expand and contract when charging and discharging. You need to leave some room for expansion, don't try to force two batteries into a small area.