Before the alarm bell is rang regarding the potential fire ball of death ... take a peek at some newer technology batteries. Relocation under the back seat, for example, involves NO lead acid batteries. They DO NOT fit. They are too big. EarthX, et cet., and the newer technlogy batteries are non-toxic, they don't ooze toxic fumes, or any other of the nasty stuff which LEAD ACID batteries do. Actually, they can be mounted or oriented in any direction, even upside down (some of them, but not all manufactureres).
In regards to a trunk mounted battery, there is ample room on the passenger side rear cargo "pocket" area (or the driver side too). There is NO need to lose your spare tire. No one mentioned this, but the spare tire in a W123 is actually part of the safety features for a rear end collision. The only confusion about a trunk mounted battery is a forum member who claimed and jumped up and down it won't fit. Well, a Group 49 Battery does in fact fit. I had a battery box oversized to permit dense foam all the way around. and it still fit perfectly in the cargo pocket area.
As for all of the anticipated problems, I discovered nor had any of them.
Battery Box Relocation
I had the battery in my trunk, neatly and nicely tucked away in a homemade battery box for well over an entire year. As for charging, no issues. I ran a bunch of electrical odds and ends for my WVO system and still kept the OEM 55 AMP altenator and never a charging problem, never a starting problem, et cet. My car got totaled and that ended that until I got a new MB. The only thing I would do different is the following:
1. Thicker cable, next size up
2. Make sure you try out some Anderson connectors
3. Get 20' feet of cable and don't sweat being short
3. Think about under the back seat. Very pricey compared to a lead battery, but it neatens up the area. I initially said no way, but I was 100% wrong on that. I had to search outside of traditional batteris. The folks at Odyssey, EarthX, and a few others really know batteries, their safety issues and considerations, et cet.
Does this mod HAVE to be done ? Of course not. It's not necessary at all. But, if you are doing mod's which require turf be cleared out, then it's an option.
