Placing an extra battery (or 2)

[Petru]

I´m going to add one or more batteries to the house bank and I'm wondering how to know where to drill and how deep. The original battery brackets do not look that strong. Does anyone one have a better battery-fixing protip?
Bavaria 30 cruiser 2006

[symphony2]

I used these force4.co.uk/item/Force-4/Stainless-Steel-Battery-Bracket/932