|It never fails to amaze me that many people who own laptops are too cheap to replace the main battery. You should be replacing it after no more than about every two years if you want to be able to use it on the battery alone for a reasonable amount of time.|
If that truly is the original main battery, it's about 11 years old!!
The message may be about the main battery or the cmos battery.
A dead or too weak cmos battery probably will not prevent the hard drive from booting and you getting into your operating system if the main battery is okay, but you may need to go into the bios Setup everytime you boot when the computer has been shut down, to set at least the the date and time.
If it's the cmos battery, when you go into the bios Setup after you have shut down the computer the time and date are the defaults instead of the present ones.
Cmos batteries typically are desgned to last about 5 years. Where the cmos battery is - e.g. it may be accessed by removing the keyboard, or it may be elsewhere inside the case - and how to replace it is probably in the service manual for your laptop model, or you may able to find that info online. Replacement cmos batteries are available on the web.
If it's the main battery, this laptop is old enough that it MAY boot okay when you have removed the main battery and have just the AC adapter plugged in, but it may NOT - newer laptops certainly will NOT when the main battery has been removed.
If it will NOT boot when only the AC adapter is connected, then you must get a new main battery, or at least use a used main battery that is capable of being at least partially charged.
Laptops will NOT start up on the main battery alone unless the main battery is charged beyond a certain minimum and capable of being charged that amount, and newer laptops will NOT start up with only the AC adapter - they will start up if the AC adapter is connected AND the main battery is installed and is capable of being charged to a least a lower minimum capacity, and is charged to at least that minimum.
Laptop batteries typically work as they were desiged to for a a year, their typical warranty period, then they begin to rapidly deteriorate. By the second year, they cannot be charged to anywhere near thei full rated capacity, and it gets worse after that. They often develop internal shorts after a long time - your batterry is old enough it might be NiCad, which is a lot more prone to do that than NiMh or Lithium batteries. If it shorts internally, the voltage it can be charged to is probably a lot lower than it should be, as well as the max capacity it can be charged to lower than it should be.
You don't necessarily have to buy a main battery from IBM or Lenovo. All that's necessary is that it fits yourcase and has at least the same capacity. There are lots of clone batteries out there - some have more capacity (mah) than the original one - as long as they have a one year warranty, they're cheaper yet they are just as good as the IBM / Lenovo one. They'll all made in the same places anyway - usually China. Use the model number of your computer to search with, or the part number on the main battery.
Are you sure the AC adapter is working?
Some have an led that lights up when they're plugged into AC, or when they're plugged into AC AND have a good connection to the laptop jack. If yours has one is it lighting up?
People frequently abuse the cord from the adapter - the end that plugs into the laptop.
They pull on the cord rather than the plug on the end of the cord. That eventually damages the plug on the end of the cord, and/or the wires inside the cord near the plug, and after a longer time, the jack in the laptop the plug plugs into. The plug should not be loose in the laptop jack. The laptop jack should not be loose in the laptop case.
Laptop adapters, or the cord between the laptop and the adapter if it can be unplugged, frequently have to be replaced. Sometimes the jack in the laptop case has to be replaced.
Newer laptops often have one led on the front of them that only lights up when the AC adapter is connected to the jack, it has a good connection, and it's charging the main battery. If your laptop has one it may be elsewhere.
That led should light up at least briefly when you unplug the AC adapter from the laptop jack then plug it back in, even if the main battery is fully charged.
If it's on, it should NOT go on and off randomly when you wiggle the plug in the jack on the laptop. That indicates the plug, or the cord near the plug, or the jack in the laptop is damaged.
The led should NOT be on 100% of the time it is plugged into the jack. That most likely indicates the main battery cannot be charged, or much less likely there's somrthing wrong with the adapter.
The led should NOT be off all the time. It should come on at least briefly when you unplug the plug from the jack and plug it back in. That indicates the AC adapter is no good, or the plug or cord near it or the jack in the laptop has a major problem, or the main battery has an open connection internally.
Your laptop won't boot if it requires a main battery to be installed as well as the AC adapter if the battery has on open connection internally.