I'm wondering how long is reasonable to expect my 159 to sit before the battery drains. We haven't been driving it much in lockdown and it has twice had a dead battery after about 3 weeks sitting. Is that reasonable ?
Will start investigating a bit more closely if this seems an unreasonable amount of time.
If it's an old battery, that is not unreasonable, 3 weeks is a fair bit of time for it to just sit.
One thing you should understand, once a battery has been discharged to dead flat it will never recover to full capacity, no matter how much charge you put in it or what colour the indicator window says.
My suggestion would be to go to Battery World or similar & pick up a new quality battery along with a little smart charger to keep the battery topped up and in good working order while it's sitting. They will let you know what you need and how to hook it up.
Same issue. Happens in lockdown... Perfect excuse for an upgrade.
Now have a Varta F19 that is much bigger than OEM (the front of the tray is open-ended) fitted with the obligatory CTEK connector.
Also changed the nine year old (and still cranking) Mercedes OEM battery in my wagon with a Varta E44. The thoughtful design enabled the tie-down clamp to be moved, again enabling fitment of a bigger battery.