Battery won't charge

Yes you can. On tools, 18 volts is 18 volts. Tools don't 'know' how the power is being created, either by Ni-Cad or Li-Ion means. Chargers are totally different. Most Li-Ion chargers can charge older Ni-Cad and some Ni-MH batteries but older Ni-Cad chargers will charge Li-Ion battery untill they overheat and sometimes start on fire because older chargers can't detect when the Li-Ion batteries are full.

li-Ion batteries have a bad habit: whenever fully depleted, they lose a few cells, to the extent that they might not be able to hold a full charge if enough cells are damaged. In other words, repeatedly using a laptop (or any other Li-Ion powered device) to battery depletion can shorten the battery's life significantly. You might want to keep the batteries fully charged whenever possible and avoid fully depleting them too often.
There is also the habit of "re-setting" the batteries by using the "fully deplete-fully charge" procedure. It only applies to niMH or NiCD batteries ( and is used to erase the "memory effect" ) but is damaging to Li-Ion batteries for the reason mentioned above.
so if your battery can not full charge,this mean you need change a new battery for your laptop
http://www.aulaptopbattery.com.au

Maybe the AC Adapter Power Cord is not working. If you can't get on the laptop with the power cord then it is bad and the battery might be drained so you have no power source to power up the laptop.
If the laptop works only off the Power Cord and the batteryis not charging, then the battery is dead.

To check to make sure the Power Cord is working remove the battery and let thelatop run for 10 minutes or so.

To check to see if the battery has any charge left in it put the battery in andremove the power cord. If it won't boot or shuts down then the battery is deadand needs to be replaced if the power cord is ok.

according to the schematic I saw yes you can and I think that you will be pleased with its performance, their operator manual even lists the weight of tool with this battery. Makita has a 1 year limited warranty on the Li-Ion battery that you might want to consider if you have the receipt.

It takes over 7 hours to charge, so did you leave it charge overnight?

But while the original battery is chargable, disposable replacements are not. Here is what the manual says:

{ ...
The supplied battery is a Li-ion battery. It charges while in the camera using the supplied charger. The camera can also use a Duracell CP1 disposable Li battery, which has the same form factor as the supplied Li-ion cell. HP claim the Li-ion cell will provide power for approximately 200 shots under "average" use and 100 shots with "extensive use of the LCD and flash".
Charge time for the battery using the supplied charger and in-camera charging is 5-7 hrs for a fully depleted battery. In the optional docking station, charging takes 2.5-3.5 hrs and using the optional rapid charger, charging takes 1-2 hrs. ... }

http://www.bobatkins.com/photography/digital/hp707.html

Li-Ion battery and NiMh battery have completely different charging requirements! Li-Ion battery has much stricter charging requirement and the regulator is normally design to trickle charge at 0.1 Current rating @ 4.2V and then completely shut down.
WARNING: if you use a Ni-Mh charger on a Li-Ion battery, then it will erupt and even explode and catch fire!
Bottom line is that the rescued Li-ion regulator is not designed for your Ni-Mh pack and you will never get a full charge with it and you will need a completely different regulator board: you are better off putting in a suitably sized Li-Ion battery with inbuilt regulator but with higher current rating if possible.
Hope it helps! Let me know how you go.

The difference is battery life. So just buy whichever you can afford.

try removing the large battery and powering off wall supply only...if ok, then replace battery