ML350 Trickle charger

[Mr T]

I have a 2006 ml350

Battery getting weaker every day over last 2 weeks

I've had rac out who have checked the battery and reported it as being good but requiring a recharge. I've got a ctek with a lighter adapter which I use for my 911

Can an ML battery be recharged ? Is ctek suitable as a trickle charger? Where are recharge points as battery beneath seat?

Thanks