could you please give us more information on electrical characteristics and mechanical data of the battery
that you want to purchase.
For a lower current application,
this kind of super-capacitor may be a solution. Charging a
capacitor is very easy. Working with supercaps are very easy.
I'm pretty sure there are LiIonPo batteries for what specification [size,electrical,mechanical]
that you require. But working with LiIonPo is not easy, specially it's charging circuity and loading
and switching circuity is far complicated.I think to make it work, find a NiCd battery is a middle
ground solution for this. NiCd charging is simple( it's a simple model with a one integrator and few pde's)
, I could guide you on this.But don't ask me how to charge LiIonPo, because I simply don't know and may be
http://batteryuniversity.com/ community could help you on this.
WARNING: Failing chances of a LiPoIon battery is very low. But when they fail, they ignite very violently.Overcharging
conditions of NiCd will release oxygen( there is a vent for that). and also NiMH will give you hydrogen.So your responsible
to double check your model,implement overlay functions.And do it your own risk. I'm already warned on this,and this is it. and I'm independent of any responsibilities and that's it.
For your mechanical requirement, I suggest this. This is known as a coin battery. And charging this is also
simple.