When is a good time to replace the battery?

[JEDI]

Bought a refurbished Latitude 3379 directly from Dell a few years ago.
It used to give me 3hrs battery life.
Now it's down to 1 1/2hrs.

When is a good time to replace the battery?
(Probably going to buy a generic one from eBay or should i buy OEM when Dell has it on sale?)

 

[georg34]

Battery life one and half hour seems pretty fine. Still your laptop batter retains 50 percentage of it original capacity.

If I were you, I would go for a power bank instead of new laptop battery.

 

[Muadib]

You lost 50% of your capacity. I'd say the time is now.