Lets understand the Sony T90 first.
It uses a rechargeable Lithium battery.
The battery is rated (by Sony) for 220 images per charge.
One of the leading reviewers said they only got 90 images per charge.
Most of the "T" model Sony cameras have a very thin battery.
Those thin batteries are not looking too good.

NiMH batteries:
Your old batteries have probably lived past their prime and they should be replaced.
I suggest you get one of the "precharged" sets of NiMH AA batteries.
They are better at not losing their charge when setting idle for long periods.
Kodak sells their "precharged" at WalMart and other chain stores.
If it were me, I would replace the charger too.

Alkaline AA batteries will only last about 40 images.
But they should not lose any charge just sitting in the camera.
If they do, you likely have a camera problem.

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