Car hesitates when starting back up

[Hazmatte]

Hi all. I am having trouble with a 2005 g35 sedan. I replaced the battery today and started the vehicle to check the alternator. The alternator is fine which is great. However when I restarted the vehicle to check the charging level of the alternator the voltage dropped to 10vdc from 13vdc and it seemed like the engine was seized from the strain it was under to start. Once the engine was turned off after testing and rested for 5-10 min. It was unable to start ?? Again the engine was struggling to start and all power was diverted to attempt the failed start so I stopped not to continue and drain the battery too much. Any ideas guys??? What should I look into next ?? I am being told the starter solenoid is causing the problem and I need to replace the starter. Any help or suggestions are appreciated to help me make this car more reliable on start ups. Thank you

[joe603]

Make sure the battery cables are on tight without any corrosion.

[Gilley]

Make sure the new battery isn't discharged.

[Hazmatte]

Cheers, I will definitely look into that guys. Thx

[audtatious]

Could be a starter problem as well. I had one go bad and it would drain the battery almost immediately...even a new one. Had it bench tested and they said it was trying to draw over 100 amps.