Essentially, Nobody knows for sure how long lithium cells will last in all radio's. Most ICOM's should be close to 40+ years, because of the cell and how they are used. The Lithium cell makers, say they will last 7 years on the shelf, just to throw a figure out there. It turns out 99% of lithium cells are rechargeable, most recharge at a very slow rate (pico amps) not practiable to mention. It is also true, Silicon diodes leak, real leaky ones they call zeners. ICOM uses a silicon diode to isolate the lithium cell from the 5v buss. So in essentially, as you use the radio, the cell is recharged. This isn't the absolute case for all radio's, but is true in ICOM base stations.
Ok, for a solution. Roberto Nardo is a fellow in Italy who is making a ROM/RAM card for $57.50 US plus shipping for your IC 271, 471, 745, 751, R71, 1271.
We will stock the popular models. Cost $57.50, plus $5 Insured First Class Mail Shipping. The card is a direct replacement so it just plugs in. If you don't feel comfortable installing it, we can install this card for you for no labor plus return shipping. ( about $30 if you want the alignment made/checked also )
If you are wondering, ICOM is charging about $50 to replace the battery and reprogram the origianl card right now.