Increase battery of a portable usb charger?

I have a  portable usb charger that has these specs:
Li-ion 3.6V    1200 mAh
Input: DC 5V    400 mAh
Output: DC 5V    450 mAh

Can i add an old battery that has 3.7V and 1150mAh to the charger and increase the battery life of it?
Would it be safe to just hook up the the negs to negs and pos to pos?
Also what would be a better way to increase battery of the charger without buying a new unit?

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Yes adding a second battery in parallel with the first will give you longer battery life.
yitmat (author)  mpilchfamily5 years ago
Could i add as much batteries i want without it affecting the output? I have a few spares 3.7V batteries here. Would i need to add a resistor or regulator to it?
Taking positive to positive and neg to neg is probably not a good idea with Li-ion batteries. My understanding is that eventually one of these batteries will be out of sync when charging, and the charger will attempt to charge the lowest-charged battery (and overcharging, sometimes explosively), the already full battery...
yitmat (author)  astroboy9075 years ago
Is there a way to by-pass this other than individually charging them?
balance the impedances (I think(. Don't exactly know how to do that though... lol
Add as many batteries as you want to increase the run time but you will want to remove them and charge them individually. So splice in connectors to make it easier to attach the batteries then remove them for charging.
yitmat (author)  mpilchfamily5 years ago
Is there a way to recharge without disconnecting from each battery? Could a battery switch between the wires for each be a solution? If a power switch is the best way, could you aid me in which types to buy and how to connect if it isnt much trouble?
Re-design5 years ago
You should only add another battery if it is exactly the same type and size. lo-ion batteries don't like to be mixed up in different sizes.