blue ant interphone questions

Hi folks, I have a pair of blue ant bluetooth wireless intercoms for talking rider to pillion. Great gadgets but battery life sucks. 3hrs if we're lucky which is just way to short for even an average ride.

The power to each unit is from a 350mAH lithium polymer battery.
Now my thoughts are to make a battery pack for each unit so I have hooked (soldered) up 3 x 1.2v 2450mAH rechargeable batteries in series.

Now from what I can gather so far this will power my units for considerably longer than the original battery. I hope I am on the right track so far.

But and there is always a but. How can I charge up my battery packs when I need to. Any advice would be fantastic.
Thanks in advance.
Wilky

Why not just use a single larger lithium cell? Lithium chargers will generally charge a larger capacity pack over a longer period of time. NiMh's don't charge the same way was Lithiums do so you have to charge the battery pack outside of the transceiver

Sceadwian, first up thanks for the reply, best I explain myself here, total ludite when it comes to electronics, happy to put things together but need big time instructions first.

So
Why not just use a single larger lithium cell? I have absolutely no idea. It was suggested to me to use the NiMHs so that was the path I started out on.

As for recharging, the packs will be external to the intercom units. I will have them hooked up with an external plug.

It'd be easiest to simply replace the existing lithium pack with a higher capacity one.

Sceadwian.
I hope you will bear with me here. If I use a larger capacity lythium polymer it will not fit inside the units enclosure.
From googling lithium batteries I figure they come as a 3.7v and as the mAH is increased so does the size of the cell.
So basicaly what I am after is something that will power my units for at least 8 -10 hours.
Can you tell me if i stick to the rechargeables that I have now hooked together is it going to work. If it is then when they go flat I will just pull them apart and charge them singular in a normal NiMH charger.

Thanks for any help you can give me.
Ta Wilky

Anyone out there can help me?