Nickel Cadmium batteries tend to remember a lower capacity setting and don't retain a full charge over time. This usually happens as a result of recharging the batteries when they haven't been fully discharged.
To rectify this, try putting the suspicious battery in the freezer for about 4 hours. This will often erase the 'memory' and allow the battery to charge to its full capacity.
If that doesn't work, you'll need to just throw the battery away and replace it. The fact is, even the best batteries will only survive around 500 discharge/recharge cycles. That means that eventually, you'll have to buy some new Bosch drill batteries - or whatever your drill happens to be.
Of course, other than a battery going bad, there are other reasons to have spare batteries on hand. For example, let's say you're screwing in a new deck. Further, let's say you're using 3" screws. That's going to put quite a strain on your batteries.
With today's quick charge chargers, if you have just 3 Bosch drill batteries you should be able to start out with 3 charged batteries and keep working non-stop all day long. When you discharge the first battery, start charging it right away.
By the time you discharge the second battery, the first probably won't be completely done, but at some point when using the 3rd battery, the first will be charged. You can then start to charge the second.
You will probably be able to keep that cycle going over and over again and stay moving all day long.
Bosch drill batteries are available as OEM replacements as well as third party, aftermarket parts.
Just make sure you buy high quality batteries. Otherwise you can damage your drill.