Exchangeable battery/accumulator level measurement

[snx]

Hi,

My task is to measure the level of a battery (non-rechargeable or rechargeable). In the usual cases where the battery would be encapsulated in a product (mobile phone) one could use a host-side "battery gauge ic", in  case of an exchangeable battery pack (cordless drill) one could use a pack-side "battery gauge ic".

However, my situation is different. The design should allow the removal of a battery from a battery holder. The battery type is  "16340" which is half of an 18650 battery. Therefore either a host side or pack side gauge ic can't be used.

The following actions are physically possible:

- User replaces empty battery with full battery
- User replaces empty battery with particially charged battery
- User replaces battery with accumulator or vice versa (full or particially charged).

My application does not need a extremely accurate form of charge-level (like 87% known from mobile phone). I only need a rough indiction like 5%,25,50,75,100 that can be deliverd to a microcontroller and should be possible to read continously.

What solution could there be for the problem?.