I purchased 00 DC 81 in the end of 2000, taking delivery on December 29th. To the best of my knowledge the two 12V batteries in 00 DC 81 had been there since it had been rehabbed around 1994 or 1995. They were in good shape, and held a charge reasonably well. I quickly learned that leaving my Larkspur C42 radio connected to the power cable the batteries slowly dropped their voltage. (Note: If you have a C42 radio the power supply meter will show your system voltage while it's plugged into the 24V system).
I looked around for a 24V battery charger and came across a unit that had been designed and sold for use with an electric bicycle! This charger delivered a charge voltage and then tapered off to a "float", or maintenance voltage when the battery was charged (about 27.6 volts, which happens to be twice the full charge voltage of a 12V battery at 13.8V). I installed a two prong Lucas accessory plug on the charger and plugged it into the accessory socket at the left rear of the crew compartment.
All went well until spring 2006, when I noticed that the charger was not delivering the float voltage. I decided to look inside and was met with a strong, STRONG smell of battery acid! I narrowed the problem to the battery under the air cleaner, which is always a difficult one to service. The bottom line is that I had not checked the battery for its electrolyte level and having run way low, generated hydrogen gas and had blown up!
Off to the auto parts store where I picked up two of the Optima "Yellow Top" batteries. These are lead-acid "spiral wound" and are maintenance free.
They can be placed into a vehicle and aside from maintaining their voltage, you can forget about them. They also have a very low "self discharge" rate and keep their charge quite well.
Then I had battery charger problems. I noticed this month (January 2007) that the charger was not alternating between its green and yellow LEDs. Only the yellow was on. The cycling meant that the float was being maintained, but the yellow only meant trouble! The charger had died. Hmmm. Time to look for a replacement.
After a siginificant search on the Internet and talking with an Optima Service Representative, I decided on a charger. It is a Soneil 2403SRE solid state charger and maintainer. (Note: This "smart charger" can manage input voltages from 90VAC to 264VAC, making it truly a "world-wide" device). I purchased mine in the USA from http://www.batterystuff.com/ , which was very prompt with shipping and answering questions.
I fitted the bare ends of the 24VDC lead with the Lucas plug from the old charger and I'm back in business! You may want to consider this charger for your Ferret ($63). It is not a "cheapie" from Auto Zone, but it will keep your two 12V batteries at 27.6V, PERIOD.
To look at the product specifications (which are very complete) CLICK HERE.