Do rechargeable batteries eventually lose their capability of recharging. I've been using the same 4 batteries for the past 22 months and in the past few months they onlhave enough life for a few pictures.
Yes, rechargable batteries lose much of their capacity over the time and over the charging cycles.
How quickly they go into bad condition depends on
- the battery system (mostly NiMh or Li-ion)
- the quality (brandname types usually provide better lifetime than noname types)
- the charger
When you are operating your camera with 4 removable batteries they are most likely NiMh cells and you should NOT use the cheapest charger to charge them. Cheap chargers often only charge the cells "by time and batterie size". Very bad system. Cheap chargers are battery killers!
Some chargers charge with a delta voltage system, sometimes called ΔV, delta-V or delta peak system. Delta chargers are the best for NiMh cells. But some simpler chargers of less quality are bundling 4 cells 2and2 (you recognize these because they only can charge 2 or 4 cells at a time), so that the delta voltage is always measured for 2 cells at a time. The best chargers for NiMh have delta voltage charge control for each single battery.
When using 4 batteries in the camera, there is another problem: If three batteries are OK and one has much less capacity, then the camera will stop operating when this one defective battery is empty. So it would be nice to find out which is the real capacity of a battery (not the nominal capacity printed on it).
Some delta chargers can also do "testing mode" and test the real battery capacity. When I find that my camera batteries become empty too quickly and I do the test, I most likely will find that 3 batteries have a capacity of around 1800 mAh or more and one with only 500 to 800 mAh. So the camera stops working when the one bad battery is empty. If your charger can test the battery capacity, you would be able to select and replace only the defective battery. Otherwise: Replace all four batteries. And replace the the charger if the batteries are NiMh and your old charger is not using the delta voltage system for each single battery charging.