[Q] connectiong external battery directly to internal one.

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Is it possible/safe to connect an external battery of same voltage but different mAh directly to the internal battery of a tablet to raise its mAh?

I am thinking about moding a tablet case to have a built in battery pack for my Iconia a500 tablet. I can easily squeeze 4 cell phone batteries in between the folds and make two 3.6v 3000mAh(or higher) battery pack with out adding much bulk or weight to it. can probably squeeze a usb hub in there too while i am at it.

I looked at the internal battery and it looks like i can splice its wires and add a connector to hook to the two 3.6v packs for easy connection.
I don't know much about electronics, but from my limited knowledge and layman point of view, as far as the tablet is concerns, it will just have a higher capacity battery, wont it?

can it be done safely without any other electronic components?

I'm not expert in that matter, but I think there's LiIon battery, and AFAIK it may make some confusement to your Fuel Gauge IC and Battery Charging IC, as these are probably calibrated to work with that certain battery type and capacitance. But I don't believe it may damage something if you connect it paralelly.

I would be careful with that if I were you. While it seems simple enough, batteries are much more complex than just voltage and capacity.

Most of the time, external batteries just go through the charging connection of the device so it can handle the power itself. If you connect it directly, you may bypass some part of the charging circuit (often times there's a circuit in the battery itself). Basically, I'm thinking the batteries may not fully charge or one will overcharge. It really depends on how it's set up. I'm not an expert with the design of rechargeable batteries though, so it may be safe.

In short, I would suggest connecting the batteries to the charger to extend your battery life. I'm sure others can offer additional insight.

A good read about batteries: http://batteryuniversity.com/learn/a...configurations

I can't comment on if it will work or if it is safe..

cellphone batteries have a built in protection to prevent them from overcharging or discharging, don't they?

The problem i have with connecting to the charging port is that it needs 12v. connecting 3 or 4 of battereis will give me either too little or too much volt. cant get 12v out of 3.7v batteries with out some kind of additional electronic parts to regulate the voltage. I don't have the sufficient knowledge to do that. this is why i figured ill do it directly. And charging would be simpler too if i can use the charger to charge both the internal and the external batteries at the same time.

Was hopping to hear from someone who did that already. I guess no one is brave/dumb enough to try it.

Sounds intresting looking forward for it

In a "perfect" environment this would be possible.
The inner resistance and voltage difference of the different batteries would even out the different capacity while charging.
You can avoid having these currents between the batteries by using diodes to separate the charging currents.

However my recommendations in terms of reliability, safety and efficiency is to use two or more batteries with the same capacity and dis-/charging curve.

is it the phone or the battery that cuts current when the battery is fully charged?

Originally Posted by ridethisbike

is it the phone or the battery that cuts current when the battery is fully charged?

On most phones tablets etc. it's the device that cuts off the charging current when the battery is fully charged.
However nearly ever batteries has also a protection circuit that cuts off the battery in case of
under, over voltage and over current, sometimes even over temperature.

Originally Posted by samotronta05

On most phones tablets etc. it's the device that cuts off the charging current when the battery is fully charged.
However nearly ever batteries has also a protection circuit that cuts off the battery in case of
under, over voltage and over current, sometimes even over temperature.

ah, well it seems to me that if the battery has to take action, then you're doing it wrong.

I'm not sure exactly how diodes work so I can't comment on that, but definitely use like batteries (two 3000mAh batteries as opposed to one 3000mAh and one 3600mAh) as to not confuse the device about the charge, causing the 3600 to not get fully charged. just make sure they get connected properly (in parallel) and it should work just fine.

in reality its no different than someone using 4 car batteries to power their car audio system. as long as its done properly (in parallel), there is really no harm.