Charging a rechargeable battery from another DC battery source..

[JonathanAnon]

I have a battery from a model airplane that needs to over 10v before it's seen by it's own charger... It is currently reading 3.54v... Is it possible for me to boost this hooking it up to a DC 9V battery, similar to the way you would jump a car battery.. I know that there is no alternator to charge it, but would they try to equalise if I hooked them up in parallel..

 

[(*steve*)]

You may be able to use a current limited supply to slightly charge the battery first.

If this is a lithium battery then you may have damaged it by allowing it to get this discharged.

Connect a (say) 12V DC source via a 1k resistor to the battery pack (+ve to +ve) and measure the voltage over time. If the battery can be recovered you should see the terminal voltage rise relatively swiftly (even at low charge rates). Stop when it gets to a little over 10V and try again with your normal charger.

If it rises to (say) 8V and won't go higher then you may have one or more damaged cells.

 

[JonathanAnon]

Hi Steve, thanks for you your response...

The use of resistor is what has me confused.. Obviously I will want something to limit the current, but then I got to thinking, when I jump my car I just hook up - to - and + to + .... with NO resistor... Is there a built in resistance in the jumper cable?

 

[(*steve*)]

Yeah, the resistance of the cables and the connection limits the current. Also the batteries are fairly happy (may vary somewhat) to charge and discharge at relatively high rates. Also, they're much larger, heavier batteries than you probably use in your model.

You haven't said if your batteries are Lithium. If they are then they require very careful charging if discharged too far.

 

[JonathanAnon]

You haven't said if your batteries are Lithium. If they are then they require very careful charging if discharged too far.

It's actually my brother's model airplane... I dont fly .. I have to check with him tomorrow, as there's no marking on the battery at all.