I am currently designing a battery powered system that will be driving a motor for roughly 1 second, hundreds of times a day. The current system runs off a two cell LI-ion 7.2V 3000mAh battery pack. Judging from some initial testing it looks like we will not be able to run for a full day using this pack and need to incorporate a solution to last longer (running the motor can draw as much as 6A). The system is also waterproof and therefore a replaceable battery introduces some complications with sealing so we are looking to add an external battery to the system.

If we must go with an external battery that switches on only when the internal battery is dead, does it also need to be Li-ion or is it okay to us a Li-polymer? The external battery would also need to be charged without being removed from the system, is it possible to charge the external battery from the same charging port and just switching the charge current to go to the respective battery? The batteries would be connected at two opposite ends of the system (there are about 6 boards connected together through cable and the internal battery would be plugged into board 1 while the external would be connected at board 6, charger connected at 4)

Is this even a possible solution or should we look into waterproofing a replaceable internal battery? Any suggestions on how to implement the two battery system? It is also a class 2 medical device so emission and reliability are of concern.

 

Why not just replace the smaller Battery with a larger Battery ?
Is this for a Commercially manufactured Machine ?,
or is it being purpose-built for a specialized application ?

No matter what type of Battery You use, it will need replacement about every 3 to 5 years,
and its Life-Expectancy will depend upon a carefully designed Charging-System and Battery selection.

Depending upon the details of the machine in question,
and your space and Money budgets,
there are Battery solutions that can run this type of Load for a week straight without recharging.
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