

As you add more compute per user interaction (“smart” features), you increase power consumption. To keep an 18hour discharge cycle, you have to have more battery. Since phone thickness is a negative marketing feature but increased screen size is a positive marketing feature, you end up with bigger phones.
Every time they reduce compute power consumption, feature inflation overtakes the gain and more power is needed over time. Try turning on battery saver in the morning… even with “normal” use the battery will last significantly longer due to disabling background power consumption.
Just to second that, the model series is Latitude, not Inspiron. and yeah, the i5 processor options I got over the years beat the i7 on processing power. The Precision models are a step up, but not any kind of low cost and seem not quite as tough.