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. Try to use it in battery savor mode or change the default low.

Change the Default Low and Critical Laptop Battery Levels

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.