RE: She DUMPED @ 4.5!
You can only speculate what the battery voltage was at the time of the lockout. If you had a logging meter attached during your setup you could see low voltage spikes, short of that, all is pure speculation.
When a 4 cell battery drops below 4.8 volts it is depleted. Many people think that battery voltage sinks away as a linear process, but this is not true. After the pack drops below 4.8 volts, and especially down to 4.5 volts, there is very little current left in the pack. Very small changes in load will bounce that pack up and down significantly.
After the lock-out there is a reduction in the load. The battery has a chance to "bounce" a little. You put a relatively small and consistant load from a hobbico voltmeter for 15 sec. and you may see a steady 4.5 volts for that period of time. If you had held it for a minute or so, I can assure you it would haver dropped way down.
Then you pull it out of the circuit, another chance for a little "bounce", then you make a quick test again and it looks like 4.5 volts.
Then simple fact is that you were trying to test a "dead" battery. Once you drop down to less than 4.8 volts with a 4 cell pack the battery is dead. Voltage readings mean nothing a 4.5 volts except the battery is dead.
If you lay that pack aside for half an hour, nothing connected, you will get a no load reading of about 4.8 volts. And a loaded reading well above the 4.5 you were reading, but only for a short time.
Try it some time.