Hope you can help. Have had problems with the bus ignition batteries, which don't hold power very long since they were fitted.

I'm told they are 655 batteries. 12 Volt

Think they are 120 - 130 Amp with extended height.

New AEC engine needs maximum power to turn it over, which adds to the mix.

I have room for 2 batteries which are 655 length and width and roughly recall the ones we filed had extended height of about 3 inches

My question is, what is the highest Amp batteries (with extended height if necessary), which I can fit?

Also recommended brands would be very helpful.

Many thanks

My bus number (if any): RCL2259

I am away for the weekend so cannot get full details however when I needed new batteries urgently I couldn’t get the size or type I wanted. What they had were 12v batteries the same size as the 1980’s 6v batteries. I bought 4 at a little more than 2 larger batteries and series parallel connected them. They sit nicely with the proper retainers, correctly filling the crate. Had no issues with this. Will take some pictures next week.

My bus number (if any): M1001, RML2276, T806

Thank You for your kind reply.

My current setup leaves me room for two 12 volt batteries with a footprint of the 655's length and width, leaving room for extended height if necessary.

I'm told most of these Route Masters run on two 12 volt.

I need as many Amps as possible to turn over this rebuilt AEC engine, which runs fine once started.

Can I ask, what was the total amperge generated by your solution of four 12 volt batteries, 6 volt size?


Again thank you for your kind reply.

My bus number (if any): RCL2259

"Don't hold power very long". Do you mean that the measured voltage and Specific gravity decay or just that the engine doesn't turn over fast enough to fire? These are two different things. The first will lead to the second but the second doesn't necessarily mean the first.

Hello Robert

Firstly look at what Roy said. It may not be a battery issue.

Secondly, I may not have been clear. I had 2 x 12V batteries wired in series. I now have 4 x 12V batteries in a series/parallel set up to give 24V but double the capacity.

The 1980's conversion to 4 x 6 volt batteries wired in series had the battery crate converted slightly from the original 3 x 8V LT manufactured batteries layout. As these 6V units (the number escapes me) are prohibitively expensive if available at all many simply changed to 2 x 12V. I have seen so many different types with a wide range of sizes and ratings.
The two batteries I had were beyond help and i needed new ones urgently. I could only get a much physically smaller (than I had) battery off the shelf and locally to me. They had two 12V 664HD and two 12V 663HD types in stock the difference being the terminal layout. In a moment of possible madness I purchased all four at around £90 each plus VAT which was a bit more than the two larger units I was looking for but not beyond reach.

The differing terminal layout helped because it allowed me to fit two with positives on the outside of the bus and two with negatives. All four of these posts are linked together. The posts on the inside are two x negative, joined and connected to the main negative cable and two x positive again linked and joined to the positive cable.
The size of each battery is 345 mm long, 172 wide and 232 high. The batteries are 105 Ah to give me 210 Ah in total and the cold cranking Amps are 735 x 2 so 1470 A in total given the parallel connection of two batteries and of course 24V given the series connection of the two pairs of batteries.

Your 655HD are not to different in size except the height is 289 mm the Ah is higher at 125 but the CCA is slightly less at 720.

As Roy has said, it could be an engine issue and your batteries are actually fine. It could be failed batteries and replacements will work perfectly well. My perhaps frivolous answer gives me something that appears to work very well and to those that care, it looks like 4 x 6V when you take the battery cover off!

It should be noted that you could do what i have (assuming you still have the full battery crate space available) and treat two as standard batteries and two as additional assistance when needed. It would need a solenoid to join them fed from the charging circuit plus a manual override to join them when needed (a battery isolator switch can be used).

I would charge the batteries for a good period of time having checked levels first and topped up if needed and then either buy a battery load tester and a hydrometer to enable testing or have them tested by someone that can do it for you.

This may work as a picture or just a link or not at all

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My bus number (if any): M1001, RML2276, T806

Attempting to answer in order, the engine fails to turn over. It might move a quarter turn if you are lucky. Charge it over night and it starts a few times then runs down.

It is nor holding power to start the engine

My bus number (if any): RCL2259

If 'starts a few times' really means turns over a few times rather than the engine fires and runs, then the symptoms you describe more or less match: 1) one, or two, faulty batteries. 2)a faulty starter motor. 3) an excessive resistance in any of the connections or in the cables between the batteries at the rear of the bus and the starter motor at the front of the bus. 4) a mechanical issue causing the engine to be difficult to turn over.

If you hadn't mentioned charging the batteries overnight the possibilities might be extended to insufficient output from the alternator or a parasitic loss over hours. Dirty batteries and especially damp, dirty batteries can discharge themselves over a few days. If the vehicle has an analogue tachograph which has been left parked with the mode switches pointing to anything other than rest then the batteries will discharge remarkably quickly.

It is also worth noting that there is a quite marked increase in cylinder surface area between an AV690 and AV760 and even more so to an AV590.

Start as David said and described by properly charging and load testing the batteries. An infra-red thermometer gun will help to locate a poor connection without the risk of burning one's hand.

Many thanks for all your positive suggestions. Found the most powerful 655 batteries, 142Ah, installed them and they work. Engine starts no problem. Am posting another thread to isolate a further question.

My bus number (if any): RCL2259