C172RG pilot reported an electrical failure during cruise. The pilot diverted and under a Mechanic's suggestion; made a gear up landing.

Narrative

Departed ZZZ1 for ZZZ2 at XA:05 for a 40-minute 89-mile flight. About 4 miles south; contacted ZZZ Departure for flight following. Within a few minutes and after radar contact; I had an electrical failure and all my radios failed. I cycled the battery/alternator switch; which didn't help. I then decided to extend the gear with the remaining battery power as I figured that would be depleted soon as well. Only the left main and nose gear extended. I heard a minor thump noise during the extension. I then got out the checklist to manually extend the gear which also failed. I then turned off the master switch and phoned my A and P Mechanic. He had me try a couple high G pull-ups to no avail and suggested I try to retract the remaining gear and land gear up. I decided I'd divert to ZZZ which has 2 runways so I wouldn't shut down ZZZ2; which is a 1 runway airport. We phoned ZZZ Control Tower and told them of our situation. He said he'd roll the equipment and I was cleared to land on [Runway] XXL. I pulled the mixture and checked battery was still off on short final and made a gentle landing.It took several minutes for an Operations truck to pull out to the runway and another 4 - 5 minutes for a fire truck to pull up. I was disappointed to see the slow response time of any assistance but fortunately there was no fire or injury and relatively little damage to the aircraft.