Yep, what you said, Dan. Chargers vary a lot, from cheap ones that actually kill batteries unless they're not watched/monitored very carefully, to combination analyzers/chargers.
Some folks (way too many) are still mentioning the negative issue of so-called "memory effect", when there was no real effect.. it just doesn't apply to rechargeable cells. Misuse and neglect are responsible for poor performance from good quality rechargeable cells.
The trouble with many battery pack temperature/thermal switches, is that they're often selected for safety (shut off in case of charger failure to prevent excessive pack temperatures/fires), and are typically in the 65 C/149 F range, which is too hot.. the cells are very likely being damaged at those temperatures. Many of the thermal switches are sensing air temperature within the pack case, not the actual cell temperatures, where the cells' core temperatures will likely be extremely excessive and rapidly damaging the cells.
One aspect of using new replacement cells, which isn't always mentioned, includes several/numerous charge/discharge cycles of new battery packs before putting them into service. The new NIMH sub-C and D cells that I started using show significant performance improvements (actually measured, not guessed) after 5 to 10 cycles. Some of the MRC charger models mentioned earlier, have controlled discharging capabilities which will show how many mAh have been drawn out of battery packs (also how many mAh have been added during charging).
Discharging of rechargeables should never include running the cells down to nearly dead.. regardless of what anyone says. Discharge cycles should be a controlled, specific to the Ah capacity, current draw to bring the charged cells down to about 80% of fully charged (to about 1V or not below 0.6V per cell, at most). These discharge levels are from cell manufacturers and data from real scientific study approaches where the goals were peak performance and long-term reliability.
For critical applications, such as endurance performance competition (not kids with RC toys), individual cells are thoroughly tested and matched before combining them into battery packs, prior to use.
Users that believe that they're saving time by not changing out battery packs, or getting the most per charge by continuing to run a cordless tool (or other rechargeable-powered device) until it just won't work any longer, are sacrificing the life of the cells.. this is one reason why many newer electronic devices shut down before their battery is depleted.