Hi iam also looking to use one of these because of having no room for a normal one. This is what I found.

Varley Red Top Racing Batteries offer an extremely high power to weight ratio. Combine this with a high resilience to shock, vibration and G-force, and you have the most desirable characteristics sought after in Motorsport. For this reason, Varley Red Top batteries are used by some of the biggest names within the industry such as Van Diemen, Tatuus Racing, Mitsubishi Motor Sport, Red Bull F1 and many more, making Varley Red Top the most popular and professional racing battery on the market.* Varley Red Top motor racing batteries are available only through specialist motorsport distributors who understand the various requirements of the different racing series and are technically capable of supporting the user.

I asume it depends on heaters/ aircon etc. What drain there is on it. I only need mine to start the engine, I think it would be ok for me.