If you get a red battery display immediately upon starting the car, but no additional error messages, then you need a new auxiliary battery. The aux battery is located under the hood, underneath the cabin air filter. The aux battery supplies backup power to the SBC brakes in the even of a fault with the main battery. It was supposedly deleted on later 211 models when the SBC was replaced with conventional brakes.

The aux battery is a standard powersports (motorcycle, etc.) size AGM battery. Different manufacturers use different terminology, but it's a GTX-14BS or equivalent. It is readily available at McParts stores such as Pep Boys, Wally-Mart, and AutoZoo. Do be aware the batteries are shipped dry; you have to add the acid, let it absorb into the AGM, then seal and charge the battery before installation.

If the main trunk mounted battery is low, the car will either not start (duh) or will give an error message to the effect that electrical consumers have been disabled. Your heated seats will be disabled and your blower fan will be restricted to low speeds. When the battery reaches a sufficient level of charge, all the toys will be enabled. I have seen this message after letting the car sit for an extended period of time, such as when traveling overseas on business.

Cheers,

- JimY