Same battery and same pump since 3/2007.
No coolant change and will run the OEM pump to 70K (55K now) and change it out with tstat and change over to Evan NPG waterless coolant.
Pumps diagnosis that I have seen so far and this isn't many of them I guess because those that fail don't do failure analysis were failure of the phenolic tube the pump is in meaning cracking and leaking or most likely short to gnd or other electrical component that failed do to heat cycles.
My M3 battery is 9 years old but I use a battery tender for my BMWs when I am not driving them and I think that makes all the difference. I have mine wired to the jump posts permnaately with the connect sitting on the headlamp housing. Takes me maybe 10 secs to hook my tender up. You might consider that if you don't drive it a lot as in a DD...
Also water pumps (excluding the 318) have failed on E36/46 at around 50-80K miles and many times resulted in a head gasket failure unless you were very lucky.
Water pumps seem to be not a component has yet got right...