I have two lithium ion batteries. One is 3.7 volts, 1200 milliamp and the other is 3.8 volts, 2600 milliamp. Can i wire these in parallel and use the charger for the 3.7 volt battery to charge both. My purpose is to extend the play time of a Bluetooth speaker I have. the 3.7 volt battery was the speakers origanal battery and the other is a Samsung cell phone battery. it has 4 connectors marked as follows: +; blank; -: Blank. \i connected to the + and - terminals.

Thanks

 

You shouldn't use or charge in parallel.

 

care to elaborate?

 

When batteries are used in series or parallel, the batteries should be of the same type and same relative condition.

If you use them in parallel, the lower voltage battery will be a load on the higher voltage battery until their voltages equalize. When the lower capacity battery runs down, it will load the higher capacity battery again.

 

Ok. So whats the best and worst that can happen? Can i use them together and charge them separately?

 

If you use them in parallel, the worst that could happen is that one would short and cause a fire/explosion.

Best case depends on the relative charges and wear state of the batteries; you might get 2X the runtime of the smaller battery.

 

Thanks. I am using them together now but not charging them. From your coments I will charge them separately. Can the charger for the 3.7 volt battery safely charge the 3.8 volt? They are both lithium ion batteries and as far as i can tell use a 5 volt charger because thar both have or were charged by a usb power supply, ie: a usb wall charger or computer usb port

 

A lithium ion charger should be able to monitor the charging process for either battery.

Using batteries of different voltages and/or amp hour ratings is not recommended. Is the convenience worth the risk?

 

I work where i have no access to a wall socket to charge my bluetooth speaker. Ive been useing a 12 volt 18 am sla battery but it is rather bulky and the lition backup batteries dont last long enough. At least the one i have that i could afford. This seamed like a cheap, ie: free, way to extend the playtime of my speaker while using the backup battery for my phone of tablet. The 3.8 volt battery is from an old cell phone that crashed beyond affordable repair. It was cheaper to buy a new phone.