Strimmer Battery Options

[Jim_Lad]

Hi,
I'm looking to get a battery strimmer given I need to use it to tidy an allotment where there is no power supply. Hoping someone can help me understand the best battery set up to get. I've tried to research it to understand myself but stuggling, apologies if it's obvious.

I'm looking at the following:
Black and Decker STC1820PC 18v Cordless Grass Trimmer with 2x 4ah 18v batteries (~£200) Black and Decker STC1820PC 18v Cordless Grass Trimmer 280mm | Grass Trimmers - https://www.tooled-up.com/black-and-decker-stc1820pc-18v-cordless-grass-trimmer-280mm/prod/100042329

However there is also the Black and Decker BCSTA5362 36v Cordless Grass Trimmer with 2x 2ah 36v battery (~£190) Black and Decker BCSTA5362 36v Cordless Grass Trimmer 330mm | Grass Trimmers - https://www.tooled-up.com/black-and-decker-bcsta5362-36v-cordless-grass-trimmer-330mm/prod/100036966

Can anyone advise which is best from a power / ability to tackle dense grass / likely battery life point of view?

I might look to expand to a B&D lawn mower that would use the same batteries in future, so whilst this isn't the main requirement now, would be worth bearing in mind for any advice / decision.

Thanks in advance for any help.

Jim