Why not just plug into your cig' lighter socket & never have to charge it up?
Why have a seperate battery & charger?
I have 100psi shurflo with varistream, 80m minibore (8mm)
14 months ago my battery finally died after 6 years so i replaced it with the cheapest one i could find, 35 quid from partco, it's only about 50amp. In the 14 months so far not once has it gone flat or failed to start the van.

No mess, no hassle, just plug in & play.

Tony